JP5263773B2 - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control contact/separation between a photoreceptor drum and an intermediate transfer belt according to output by an optical sensor for detecting reference toner on the intermediate transfer belt. <P>SOLUTION: The color image forming apparatus includes: a plurality of photoreceptor drums 3Y, 3M, 3C and 3K on which toner images are carried; the intermediate transfer belt 61 where a plurality of color toner images on the respective photoreceptor drums 3Y, 3M, 3C and 3K are superposed; a contact/separation mechanism part 30 which makes the intermediate transfer belt 61 contact with/separate from the respective photoreceptor drums 3Y, 3M, 3C and 3K; the optical sensors 21 and 22 which detect reflected light from the toner image on the intermediate transfer belt 61; and shutters 51 and 52 which shield the optical sensors 21 and 22 from light and make them open interlocked with operation of the contact/separation mechanism part 30. The contact/separation mechanism part 30 controls the contact/separation between the intermediate transfer belt 61 and the respective photoreceptor drums 3Y, 3M, 3C and 3K based on output from the optical sensors 21 and 22 by light shielding-opening operation of the shutters 51 and 52. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention provides a plurality of photosensitive drums that carry toner images, an intermediate transfer belt that superimposes a plurality of color toner images on each photosensitive drum, and a separation between the intermediate transfer belt and each photosensitive drum. The present invention relates to a color image forming apparatus including a separation / contact mechanism unit that performs contact and an optical sensor that detects reflected light from a toner image on the intermediate transfer belt.

  In recent years, electrophotographic image forming apparatuses capable of forming multicolor images such as color copiers and color printers have been developed. For example, a toner image for each color is formed on a latent image carrier such as a photosensitive drum. After forming and transferring the toner images for each color on the intermediate transfer belt, which is an intermediate transfer body, and superimposing them on them to form a multicolor image, the multicolor image is transferred to a recording paper, which is a transfer paper, and fixed. An intermediate transfer type color image forming apparatus for forming an image is well known.

  In such a color image forming apparatus, the intermediate transfer belt has a mode in which printing is performed and a mode in which printing is not performed. In the mode in which printing is performed, the intermediate transfer belt is Y (yellow), M (magenta), C There are two modes: a color mode in contact with all (Cyan) and K (Black) photosensitive drums, and a monochrome mode in contact with only the K (Block) photosensitive drums. Also, in the mode in which printing is not performed, there is a non-printing mode in which all the photosensitive drums are separated from the intermediate transfer belt so as not to cause contact (pressure) stress and frictional degradation between the photosensitive drum and the intermediate transfer belt. doing.

A color image forming apparatus provided with a mechanism for separating and contacting the intermediate transfer belt with respect to the photosensitive drum is disclosed in, for example, Japanese Patent Application Laid-Open No. H10-228707. In a color image forming apparatus described in Patent Document 1, black and color photosensitive drums and a primary transfer roller are arranged to face each other with an endless intermediate transfer belt interposed therebetween, and the primary transfer roller is driven to drive the intermediate transfer belt. Is a tandem type color image forming apparatus that contacts and separates the photosensitive drum from a black primary transfer roller moving lever, a color primary transfer roller moving lever, and coaxially driving these two moving levers independently. It has a configuration including an arranged cam and a drive source that rotationally drives the cam via the shaft. In addition, a dedicated sensor is provided to detect the amount of toner on the intermediate transfer belt.
JP 2006-201338 A

  In the color image forming apparatus of Patent Document 1, a detection switch for detecting whether the intermediate transfer belt is in a color mode, a monochrome mode, or a non-printing mode is provided, and detection is performed by turning this detection switch ON / OFF. It is like that.

  In this case, since it is necessary to detect three modes (states) as described above, it is necessary to provide at least two mode detection switches in the conventional color image forming apparatus. Further, in order to detect the amount of toner on the intermediate transfer belt, it is necessary to provide a dedicated sensor. For this reason, the number of parts increases, and it is necessary to secure the arrangement space thereof, resulting in an increase in manufacturing cost.

  The present invention was devised to solve such problems, and its purpose is to control the separation and contact between the photosensitive drum and the intermediate transfer belt by the output of an optical sensor that detects the reference toner on the intermediate transfer belt. Accordingly, an object of the present invention is to provide a color image forming apparatus in which the number of parts of a mechanism to be detected is reduced and the apparatus is miniaturized.

  In order to solve the above problems, a color image forming apparatus of the present invention includes a plurality of photosensitive drums that carry toner images, an intermediate transfer belt that superimposes a plurality of color toner images on each photosensitive drum, In the color image forming apparatus, comprising: a separation / contact mechanism portion that separates / contacts the intermediate transfer belt and each of the photosensitive drums; and an optical sensor that detects reflected light from the toner image on the intermediate transfer belt. A shutter that shields / opens the optical sensor in conjunction with the operation of the separation / contact mechanism, and the intermediate transfer belt and each of the photosensitive drums based on an output from the optical sensor by the light shielding / opening operation of the shutter. And a separation / contact control unit for controlling the separation / contact of the head.

  According to such a configuration, the detection of the reference toner amount on the intermediate transfer belt and the separation / contact control between the photosensitive drum and the intermediate transfer belt can be performed using the common optical sensor. Thereby, it is not necessary to provide a dedicated sensor for each, the number of parts can be reduced, and the manufacturing cost can be reduced and the apparatus can be downsized. Further, since the intermediate transfer belt is a series of sequences in which the toner density is detected by contacting the photosensitive drum, the control can be easily performed.

  The separation control unit is configured to control separation / contact between the intermediate transfer belt and each photosensitive drum in three modes of a color mode, a monochrome mode, and a non-printing mode. That is, it is possible to control the separation and connection of the three modes using a common optical sensor.

Further, when the shutter moves to a position where the optical sensor shields the optical sensor, the separation / contact mechanism part moves the intermediate transfer belt away from the photosensitive drum in conjunction with the movement, and the shutter opens the optical sensor. The intermediate transfer belt is brought into contact with the photosensitive drum in association with the movement . Thereby, when the toner on the photosensitive drum is transferred onto the intermediate transfer belt, since the shutter is opened, the toner density can be detected.

  The separation / contact control unit causes all the photosensitive drums to contact the intermediate transfer belt in the color mode, and causes only the black photosensitive drum to contact the intermediate transfer belt in the monochrome mode. Then, the separation / contact mechanism is controlled so that all the photosensitive drums are separated from the intermediate transfer belt. Thereby, it is possible to control the separation and connection of the three modes using a common optical sensor.

  The shutter is provided on a lever of the separation / contact mechanism that moves parallel to the moving direction of the intermediate transfer belt. Thereby, since the shutter provided in the lever moves horizontally with respect to the fixedly arranged sensor as the lever moves, it is possible to easily detect the light shielding / opening of the optical sensor.

  The optical sensor is a sensor that detects toner density. This makes it possible to detect the toner density using a common optical sensor.

  The optical sensor is a sensor that detects a toner image forming position. Accordingly, the toner image forming position can be detected using a common optical sensor.

In the color image forming apparatus of the present invention, the optical sensor includes a monochrome optical sensor that detects a black toner density and a color optical sensor that detects a toner density of a color other than black toner, A shutter is provided in each optical sensor. In the color image forming apparatus of the present invention, the optical sensor detects a black toner density and a toner image forming position, a monochrome optical sensor, and detects a toner density and a toner image forming position of a color other than black toner. It comprises a color optical sensor, and the shutter is provided in each optical sensor.

  As the optical sensor, a reflection type sensor can be used.

  Since the present invention is configured as described above, detection of the reference toner amount on the intermediate transfer belt and separation / contact control between the photosensitive drum and the intermediate transfer belt can be performed using a common optical sensor. Therefore, it is not necessary to provide a dedicated sensor for each, and it is possible to reduce the number of parts, reduce the manufacturing cost, and reduce the size of the apparatus.

  Hereinafter, a color image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a front view showing the overall configuration of the color image forming apparatus according to the present embodiment.

The color image forming apparatus 100 according to the present embodiment forms multicolor and single color images on a predetermined sheet (recording paper) in accordance with image data transmitted from the outside.
0 and the automatic document processor 120.

  The apparatus main body 110 includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, a charger 5, an intermediate transfer belt unit 6, a fixing unit 7, a paper feed cassette 81, a paper discharge tray 91, and the like. It is configured.

  A document placing table 92 made of transparent glass on which a document is placed is provided on the upper portion of the apparatus main body 110, and an automatic document processing device 120 is attached to the upper side of the document placing table 92. The automatic document processing device 120 automatically conveys the document on the document placing table 92. The document processing device 120 is configured to be rotatable in the direction of arrow M, and the document can be placed manually by opening the document table 92.

  The image data handled in the color image forming apparatus 100 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, four developing devices 2, photosensitive drums 3, charging devices 5, and cleaner units 4 are provided to form four types of latent images corresponding to the respective colors, and are respectively provided in black, cyan, magenta, and yellow. These are set to form four image stations.

  The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to the charger type as shown in FIG. 1, a contact type roller type or brush type charger is used. Sometimes used.

  The exposure unit 1 is configured as a laser scanning unit (LSU) provided with a laser emitting portion, a reflection mirror, and the like. The exposure unit 1 includes a polygon mirror that scans a laser beam and optical elements such as a lens and a mirror for guiding the laser beam reflected by the polygon mirror to the photosensitive drum 3. In addition, as the exposure unit 1, for example, a method using an EL or LED writing head in which light emitting elements are arranged in an array can be employed.

  The exposure unit 1 has a function of forming an electrostatic latent image corresponding to the image data on the surface thereof by exposing the charged photosensitive drum 3 according to the input image data. The developing unit 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners of four colors (Y, M, C, K). The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 6 disposed above the photosensitive drum 3 includes an intermediate transfer belt 61, an intermediate transfer belt driving roller 62, an intermediate transfer belt driven roller 63, an intermediate transfer roller 64, and an intermediate transfer belt cleaning unit 65. I have. Four intermediate transfer rollers 64 are provided corresponding to each color of Y, M, C, and K.

  The intermediate transfer belt driving roller 62, the intermediate transfer belt driven roller 63, and the intermediate transfer roller 64 are driven to rotate while the intermediate transfer belt 61 is stretched. Each intermediate transfer roller 64 provides a transfer bias for transferring the toner image on the photosensitive drum 3 onto the intermediate transfer belt 61.

The intermediate transfer belt 61 is provided so as to be in contact with each photoconductor drum 3, and the toner images of the respective colors formed on the photoconductor drum 3 are sequentially transferred to the intermediate transfer belt 61 and transferred. Further, it has a function of forming a color toner image (multicolor toner image) on the intermediate transfer belt 61. The intermediate transfer belt 61 is formed in an endless shape using, for example, a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 61 is performed by an intermediate transfer roller 64 that is in contact with the back side of the intermediate transfer belt 61. A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 64 in order to transfer the toner image. The intermediate transfer roller 64 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 61. In this embodiment, a roller shape is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the electrostatic images visualized according to the respective hues on the respective photosensitive drums 3 are laminated on the intermediate transfer belt 61. The laminated image information is transferred onto the sheet by the transfer roller 10 which is a secondary transfer mechanism unit disposed at a contact position between the sheet and the intermediate transfer belt 61, which will be described later, by the rotation of the intermediate transfer belt 61. . However, the secondary transfer mechanism is not limited to the transfer roller, and a corona charger or a transfer belt can be used.

  At this time, the intermediate transfer belt 61 and the transfer roller 10 are pressed against each other at a predetermined nip, and a voltage for transferring the toner onto the paper is applied to the transfer roller 10 (the polarity opposite to the toner charging polarity (−)). (+) High voltage). Further, in order to obtain the nip constantly, the transfer roller 10 uses a hard material (metal or the like) for either the transfer roller 10 or the intermediate transfer belt drive roller 62 and the other is a soft material such as an elastic roller. (Elastic rubber roller, foaming resin roller, etc.) are used.

  Further, as described above, the toner adhered to the intermediate transfer belt 61 by contacting the photosensitive drum 3 or the toner remaining on the intermediate transfer belt 61 without being transferred onto the sheet by the transfer roller 10 is used in the next step. Therefore, the intermediate transfer belt cleaning unit 65 is configured to remove and collect the toner. The intermediate transfer belt cleaning unit 65 includes a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 61. The intermediate transfer belt 61 that comes into contact with the cleaning blade is supported by an intermediate transfer belt driven roller 63 from the back side. ing.

  The paper feed cassette 81 is a tray for storing sheets (recording paper) used for image formation, and is provided below the exposure unit 1 of the apparatus main body 110. A sheet used for image formation can also be placed in the manual sheet feeding cassette 82. A paper discharge tray 91 provided above the apparatus main body 110 is a tray for collecting printed sheets face down.

  Further, the apparatus main body 110 has a substantially vertical sheet conveyance path S for feeding the sheets of the sheet feeding cassette 81 and the manual sheet feeding cassette 82 to the sheet discharge tray 91 via the transfer roller 10 and the fixing unit 7. Is provided. In the vicinity of the paper transport path S from the paper feed cassette 81 or the manual paper feed cassette 82 to the paper discharge tray 91, pickup rollers 11a and 11b, a plurality of transport rollers 12a to 12d, a registration roller 13, a transfer roller 10, and a fixing unit. 7 etc. are arranged.

The conveyance rollers 12 a to 12 d are small rollers for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 12 a to 12 d are provided along the sheet conveyance path S. The pickup roller 11 a is provided near the end of the paper feed cassette 81, picks up sheets one by one from the paper feed cassette 81, and supplies them to the paper transport path S. Similarly, the pickup roller 11 b is provided in the vicinity of the end of the manual paper feed cassette 82, picks up sheets one by one from the manual paper feed cassette 82, and supplies them to the paper transport path S.

  Further, the registration roller 13 temporarily holds the sheet being conveyed through the sheet conveyance path S. The sheet has a function of conveying the sheet to the transfer roller 10 at the timing when the leading edge of the toner image on the photosensitive drum 3 and the leading edge of the sheet are aligned.

  The fixing unit 7 includes a heat roller 71 and a pressure roller 72, and the heat roller 71 and the pressure roller 72 rotate with the sheet interposed therebetween. The heat roller 71 is set so as to reach a predetermined fixing temperature by a control unit based on a signal from a temperature detector (not shown), and the toner is thermocompression bonded to the sheet together with the pressure roller 72. It has the function of fusing, mixing, and pressing the transferred multicolor toner image and thermally fixing the sheet. An external heating belt 73 for heating the heat roller 71 from the outside is provided.

  Next, the sheet conveyance path will be described in detail.

  As described above, the color image forming apparatus 100 is provided with the paper feed cassette 81 for storing sheets and the manual paper feed cassette 82 in advance. Pickup rollers 11a and 11b are arranged to feed sheets from the sheet feeding cassettes 81 and 82, respectively, and guide the sheets one by one to the conveyance path S.

  The sheet conveyed from each of the sheet feeding cassettes 81 and 82 is conveyed to the registration roller 13 by the conveying roller 12a in the sheet conveying path S, and transferred at a timing when the leading edge of the sheet and the leading edge of the image information on the intermediate transfer belt 61 are aligned. It is conveyed to the roller 10 and image information is written on the sheet. Thereafter, the sheet passes through the fixing unit 7, whereby the unfixed toner on the sheet is melted and fixed by heat, and then discharged onto the paper discharge tray 91 through the conveying roller 12 b disposed thereafter.

  The above-mentioned conveyance path is for a single-sided printing request for a sheet. On the other hand, when a double-sided printing request is made, the trailing edge of the sheet that has finished single-sided printing and has passed through the fixing unit 7 as described above. When the sheet is held by the final conveying roller 12b, the conveying roller 12b rotates backward to guide the sheet to the conveying rollers 12c and 12d. Then, after printing is performed on the back surface of the sheet through the registration roller 13, the sheet is discharged to the discharge tray 91.

  The above is the description of the overall configuration of the color image forming apparatus.

  2 to 5 show a mechanism structure according to the present embodiment, and show a peripheral structure of the intermediate transfer belt unit 6, specifically, a basic structure of the separation / contact mechanism portion 30 of the intermediate transfer belt 61. . 2 to 4 are front views and FIG. 5 is a plan view. In the following description, when it is necessary to distinguish between the photosensitive drum 3 and the intermediate transfer roller 64 corresponding to each color of Y, M, C, and K, each photosensitive drum 3 and each intermediate transfer roller 64. A Y, M, C, and K indicating each color are added to the end of the symbol to distinguish them. Further, as shown in FIG. 5, the separation / contact mechanism portions 30 (30A, 30B) are respectively disposed on both sides in the left-right direction (vertical direction in FIG. 5) orthogonal to the movement (rotation) direction of the intermediate transfer belt 61. The intermediate transfer rollers 64 are supported on both the left and right sides, but in the following description, the separation / contact mechanism 30A mainly on the front side (lower side in FIG. 5) will be described with reference to FIGS. To explain.

  Each of the intermediate transfer rollers 64Y, 64M, and 64C arranged to face the Y, M, and C photoconductive drums 3Y, 3M, and 3C is one arm of a transfer roller arm 31 formed in a substantially L shape. (Hereinafter referred to as “horizontal armband”) 31a is rotatably supported at the tip of 31a. The transfer roller arm 31 has an L-shaped bent portion 31b rotatably supported on an apparatus frame (not shown). The other arm rod (hereinafter referred to as “vertical arm rod”) of the transfer roller arm 31. ) 31c is rotatably supported by a first slide rod (corresponding to the lever described in claims) 35 supported so as to be reciprocally movable in a horizontal direction with respect to a device frame (not shown).

  The first slide rod 35 is in contact with the cam surface of a first eccentric cam 37 that is rotatably held by a cam shaft 36 on a device frame (not shown) at the right end 35a in FIG. Further, the first slide rod 35 has a first spring 32 in which one end portion 32 a is locked and fixed to a device frame (not shown) and the other end portion 32 b is locked and fixed to the first slide rod 35. The right end 35 a of the slide rod 35 is urged so as to be always in pressure contact with the cam surface of the first eccentric cam 37.

  On the other hand, the intermediate transfer roller 64K arranged to face the photosensitive drum 3K is at the tip of one arm rod (hereinafter referred to as “lateral arm rod”) 33a of the transfer roller arm 33 formed in a substantially L shape. It is rotatably supported. The transfer roller arm 33 has an L-shaped bent portion 33b rotatably supported on an apparatus frame (not shown), and the other arm rod (hereinafter referred to as “vertical arm rod”) of the transfer roller arm 33. ) 33c is rotatably supported by a second slide rod 38 (corresponding to the lever described in the claims) 38 supported so as to be reciprocally movable in a horizontal direction with respect to a device frame (not shown).

  Further, the backup roller 66 is rotatably supported at the tip of one arm rod (hereinafter referred to as “lateral arm rod”) 43a of the backup roller arm 43 formed in a substantially L shape. The backup roller arm 43 has an L-shaped bent portion 43b rotatably supported on an apparatus frame (not shown). The other arm rod of the transfer roller arm 43 (hereinafter referred to as “vertical arm rod”). ) 43c is rotatably supported by the second slide rod 38.

  In the second slide rod 38, the left end 38a in FIG. 2 is in contact with the cam surface of a second eccentric cam 39 that is rotatably held by a cam shaft 36 on a device frame (not shown). Further, the second slide rod 38 has a second end 34 a locked and fixed to a device frame (not shown), and the other end 34 b is locked and fixed to the second slide rod 38 by the second spring 34. The left end 38 a of the slide rod 38 is urged so as to be always in pressure contact with the cam surface of the second eccentric cam 39.

  Further, as shown in FIG. 5, the cam shaft 36 holding the first eccentric cam 37 and the second eccentric cam 39 has one end portion interposed through a coupling portion composed of the first gear 25 and the second gear 26. Are linked to the drive motor 27. In other words, the cam shaft 36 is driven to rotate in one direction or both directions via the coupling portion by the rotation control of the drive motor 27.

  A tension roller 67 for applying a predetermined tension to the intermediate transfer belt 61 is rotatably supported by a tip portion 45a of the tension roller arm 45, and a lower end portion 45b of the tension roller arm 45 is attached to a device frame (not shown). It is rotatably supported. Although not shown, the tension roller arm 45 is biased so as to always apply a predetermined tension to the intermediate transfer belt 61 by biasing means such as a coil spring.

  In such an arrangement, the horizontal arm rods 31a, 31a, 31a of the transfer roller arms 31Y, 31M, 31C corresponding to Y, M, C, and the horizontal arm rods 33a of the transfer roller arm 33K corresponding to K, and The back arm 43a of the backup roller arm 43 is disposed in a state of facing opposite directions.

  Therefore, when the first slide rod 35 is moved in the right direction X1 as shown in FIG. 3 from the position shown in FIG. 2, the transfer roller arms 31Y, 31M, 31C are pivoted support points of the bent portions 31b, 31b, 31c. As a result, the horizontal arm 31a, 31a, 31a is moved upward and the intermediate transfer rollers 64Y, 64M, 64C are separated from the intermediate transfer belt 61. The photosensitive drums 3Y, 3M, and 3C are separated from each other.

  On the other hand, when the second slide rod 38 moves from the position shown in FIG. 2 in the left direction X2 as shown in FIG. 4, the transfer roller arm 33K and the backup roller arm 43 use the rotation fulcrums of the bent portions 33b and 43b. As a result of rotation in the left direction R2 as the center, the horizontal arm rods 33a and 43a move upward, and the intermediate transfer roller 64K and the backup roller 66 are separated from the intermediate transfer belt 61. As a result, the intermediate transfer belt 61 is separated from the photosensitive drum 3K. Will be separated.

  FIG. 6 shows the shape and arrangement positional relationship of the first eccentric cam 37 and the second eccentric cam 39 formed integrally with the cam shaft 36. The first eccentric cam 37 and the second eccentric cam 39 are formed at positions shifted in the direction perpendicular to the paper surface in FIG. 6 with respect to the cam shaft 36. In the example shown in FIG. 39 is disposed on the front side of the first eccentric cam 37.

  The first eccentric cam 37 includes a bulging portion (large diameter portion) 37a that expands at an angle of approximately 45 degrees. In the state shown in FIGS. 2 and 6A, the center line of the bulging portion 37a is provided. It is arranged so that CL1 faces the left side in the horizontal direction (that is, the bulging portion 37a abuts on the right end portion 35a of the first slide rod 35).

  On the other hand, the second eccentric cam 39 includes a bulging portion (large diameter portion) 39a that expands at an angle of approximately 90 degrees. In the state shown in FIG. 2, the center line CL2 of the bulging portion 39a is diagonally rightward. It is arranged so as to face approximately 45 degrees upward (that is, the lower end portion of the bulging portion 39a abuts on the left end portion 38a of the second slide rod 38).

  When the camshaft 36 is rotated 90 degrees rightward from the state shown in FIG. 6A, the right end 35a of the first slide rod 35 is moved to the first eccentric cam 37 as shown in FIG. 6B. As a result of the contact with the cam surface of the small-diameter portion 37b, the first slide rod 35 is moved by the distance D1 in the right direction X1 by the urging force of the first spring 32. On the other hand, the left end 38 a of the second slide rod 38 is in contact with the upper end of the bulging portion 39 a of the second eccentric cam 39. That is, since the left end 38a of the second slide rod 38 is in contact with the same bulging portion 39a, the position does not move in the lateral direction and is kept. This state is shown in FIG.

  When the cam shaft 36 is further rotated 90 degrees rightward from the state shown in FIG. 6B, the right end 35a of the first slide rod 35 is moved to the first eccentric cam 37 as shown in FIG. 6C. The first slide rod 35 keeps the same position as the position shown in FIG. 6B because it is in contact with the cam surface of the small-diameter portion 37b. On the other hand, as a result of the left end portion 38a of the second slide rod 38 coming into contact with the small diameter portion 39b of the second eccentric cam 39, the left end portion 38a of the second slide rod 38 is moved in the left direction X2 by the urging force of the second spring 34. Is moved by a distance D2. This state is the state shown in FIG.

  The above operations are summarized as follows.

That is, when the cam is in the state shown in FIG. 6A, the transfer roller arms 33Y, 33M, 33C linked to the first slide bar 35, and the transfer roller arm 33K linked to the second slide bar 38. The backup roller arm 43 is in the state shown in FIG. That is, the intermediate transfer belt 61 is brought into contact with all the photosensitive drums 3Y, 3M, 3C, 3K of Y, M, C, K with a predetermined pressure by the pressing force of the intermediate transfer rollers 64Y, 64M, 64C, 64K. Color mode.

  Next, when the camshaft 36 rotates 90 degrees rightward from the state shown in FIG. 6A to the state shown in FIG. 6B, the first slide rod 35 moves in the right direction X1 by the distance D1. The transfer roller arms 33Y, 33M, and 33C linked to this rotate in the R1 direction, and the intermediate transfer rollers 64Y, 64M, and 64C are separated from the intermediate transfer belt 61. On the other hand, the transfer roller arm 33K and the backup roller arm 43 linked to the second slide rod 38 are maintained as they are. As a result, the intermediate transfer belt 61 is separated from the Y, M, and C photoconductive drums 3Y, 3M, and 3C, and is in a monochrome mode state shown in FIG.

  Next, when the camshaft 36 is further rotated 90 degrees to the right from the state shown in FIG. 6B to the state shown in FIG. 6C, the first slide rod 35 is in the state shown in FIG. 6B. Maintain (position). On the other hand, the second slide rod 38 moves in the left direction X2 by the distance D2, and the transfer roller arm 33K and the backup roller arm 43 linked to the second slide rod 38 rotate in the R2 direction, so that the intermediate transfer roller 64K and the backup roller 66 are rotated. Is separated from the intermediate transfer belt 61. As a result, the intermediate transfer belt 61 enters a non-printing mode state shown in FIG. 4 that is separated from all the Y, M, C, and K photoconductive drums 3Y, 3M, 3C, and 3K.

  In the intermediate transfer belt unit 6 having the separation / contact mechanism 30 (30A, 30B) configured as described above, the density of the toner image primarily transferred to the intermediate transfer belt 61 is at least near the intermediate transfer belt 61. Optical sensors 21 and 22 to detect are disposed to face the intermediate transfer belt 61. In the present embodiment, shutters 51 and 52 for shielding and opening the optical sensors 21 and 22 are provided. Since the shapes of the shutters 51 and 52 differ depending on the arrangement positions of the optical sensors 21 and 22, the arrangement structure of the optical sensors 21 and 22 and the shapes of the shutters 51 and 5 will be described below with specific examples. .

[Specific Example 1]
7 to 12 show the arrangement positions of the optical sensors 21a and 22a and the shapes of the shutters 51a and 52a according to the first specific example. FIG. 7 is a plan view of the intermediate transfer belt unit 6, and FIG. 7 is a schematic cross-sectional view taken along the line AA in FIG. 7, FIG. 9 is an enlarged perspective view of the shutter 51a portion, and FIGS. 10 to 12 are front views of the separation mechanism 30 (30A).

  The optical sensor 21a according to the first specific example is a color optical sensor (hereinafter referred to as a color optical sensor) that detects the toner density of each color of cyan (C), magenta (M), and yellow (Y). The optical sensor 22a is a monochrome optical sensor (hereinafter referred to as a monochrome optical sensor) that detects the toner density of black (K), and has a function as a registration sensor that detects a toner image formation position. Make it not exist. Therefore, in the first specific example, the color optical sensor 21a is disposed between the photosensitive drums 3K and 3C and in the vicinity of the first slide rod 35 of the separation / contact mechanism unit 30, and is used for monochrome optical. The sensor 22a is disposed on the downstream side (right side in FIG. 10) of the photosensitive drum 3K. The color optical sensor 21 a is disposed in the vicinity of one side edge (lower side edge in FIG. 7) 611 of the intermediate transfer belt 61, and the monochrome optical sensor 22 a is the other side of the intermediate transfer belt 61. It is arranged near the side edge (upper side edge in FIG. 7) 612.

  On the other hand, the color shutter 51a that shields and opens the color optical sensor 21a is, as shown in FIGS. 8 and 9A, the first slide rod of one separation / contact mechanism 30A (lower side in FIG. 7). 35, a support piece 51a1 extending horizontally from the lower side near the right end 35a, a hanging piece 51a2 extending downward from the tip of the supporting piece 51a1, and the hanging piece 51a2. It is formed of a light shielding piece 51a3 extending horizontally inward from the lower end. In the color shutter 51a formed in this way, the base end side of the support piece 51a1 is fixed to the first slide rod 35 by screws or the like (not shown).

  Similarly, the monochrome shutter 52a that shields / opens the monochrome optical sensor 22a is, as shown in FIGS. 8 and 9B, the second slide of one separation / contact mechanism 30B (upper side in FIG. 7). A support piece 52a1 extending horizontally from the lower side near the right end 38b of the flange 38, a hanging piece 52a2 extending downward from the tip of the supporting piece 52a1, and the hanging piece 52a2. And a light-shielding piece 52a3 that extends horizontally inward from the lower end of the light-emitting element. In the monochrome shutter 51b formed in this way, the base end side of the support piece 51b1 is fixed to the second slide rod 38 by screws or the like (not shown). That is, in the first specific example, the color shutter 51a and the monochrome shutter 52a have the same shape.

  The light shielding pieces 51a3 and 52a3 of the shutters 51a and 52a thus formed are arranged as shown in FIGS. 10 to 12 with respect to the optical sensors 21a and 22a.

  That is, FIG. 10 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the color mode state. In this color mode state, the color shutter 51a is in a state where the color optical sensor 21a is opened (the state where the color shutter 51a is not interposed between the intermediate transfer belt 61 and the color optical sensor 21a). The monochrome shutter 52a is in a state in which the monochrome optical sensor 22a is opened (a state in which the monochrome shutter 52a is not interposed between the intermediate transfer belt 61 and the monochrome optical sensor 22a). That is, in the color mode state, both optical sensors 21a and 22a are both in the ON state. As a result, the color toner density can be detected by the color optical sensor 21a. That is, the color shutter 51a does not hinder the detection of the color toner density by the color optical sensor 21a.

  FIG. 11 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the monochrome mode state. In this monochrome mode state, only the first slide rod 35 moves in the X1 direction from the color mode state shown in FIG. 10, so that the color shutter 51a shields the color optical sensor 21a (the color shutter 51a has A state of being interposed between the intermediate transfer belt 61 and the color optical sensor 21a). On the other hand, since the second slide rod 38 maintains its position, the monochrome shutter 52a opens the monochrome optical sensor 22a. That is, in the monochrome mode state, the color optical sensor 21a is in the OFF state and the monochrome optical sensor 22a is in the ON state. As a result, the black toner density can be detected by the monochrome optical sensor 22a. That is, the monochrome shutter 52a does not interfere with detection of the black toner density by the monochrome optical sensor 22a.

  FIG. 12 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the non-printing mode state. In this non-printing mode state, only the second slide rod 38 moves in the X2 direction from the monochrome mode state shown in FIG. 11, so that the monochrome shutter 52a shields the monochrome optical sensor 22a (monochrome shutter 52a). Is interposed between the intermediate transfer belt 61 and the monochrome optical sensor 22a). On the other hand, since the first slide rod 35 maintains its position, the color shutter 51a shields the color optical sensor 21a. That is, in the non-printing mode state, the color optical sensor 21a is in an OFF state and the monochrome optical sensor 22a is in an OFF state. That is, in the non-printing mode state, there is no problem because the toner density is not detected even if both the optical sensors 21a and 22a are both OFF.

  As described above, in the first specific example, the shutters 51a and 52a are arranged so as to be interlocked with the movement operation of the first slide rod 35 and the second slide rod 38 of the separation / contact mechanism 30 corresponding to each mode. In this mode, the optical sensors 21a and 22a are shielded from light and opened so as not to interfere with toner density detection of the optical sensors 21a and 22a. As a result, as described above, in the color mode state, both the optical sensors 21a and 22a are in the ON state, and in the monochrome mode state, the color optical sensor 21a is in the OFF state, the monochrome optical sensor 22a is in the ON state, and the non-printing mode. In this state, since both the optical sensors 21a and 22a are in the OFF state, the photosensitive drums 3Y, 3M, 3C, and 3K and the intermediate transfer belt are detected by detecting the ON / OFF state of the optical sensors 21a and 22a. The separation / contact control with 61 can be performed.

  That is, in order to shift from the color mode to the monochrome mode, the drive motor 27 is drive-controlled to rotate the cam shaft 36, and the positions of the first eccentric cam 37 and the second eccentric cam 39 are shown in FIG. When rotating from the state to the state shown in FIG. 6B, among the optical sensors 21a and 22a in the ON state, the color optical sensor 21a changes from the ON state to the OFF state. Accordingly, the drive of the drive motor 27 is stopped at the timing when both the optical sensors 21a and 22a change from the ON state to the color optical sensor 21a and the monochrome optical sensor 22a to the ON state. The drums 3Y, 3M, and 3C are separated from the intermediate transfer belt 61, and the mode can be reliably shifted to the monochrome mode state in which only the photosensitive drum 3K is in contact with the intermediate transfer belt 61.

  Further, in order to shift from the monochrome mode to the non-printing mode, the drive motor 27 is driven and controlled to rotate the cam shaft 36, and the positions of the first eccentric cam 37 and the second eccentric cam 39 are shown in FIG. When rotated from the state shown in FIG. 6C to the state shown in FIG. 6C, the color optical sensor 21a remains in the OFF state, and only the monochrome optical sensor 22a changes from the ON state to the OFF state. Therefore, by stopping the drive of the drive motor 27 at the timing when both the sensors 21a and 22a are turned off from the state in which the color optical sensor 21a is OFF and the monochrome optical sensor 22a is ON, all the photosensitive elements are detected. The body drums 3 </ b> Y, 3 </ b> M, 3 </ b> C, and 3 </ b> K can be reliably transferred to the non-printing mode state separated from the intermediate transfer belt 61.

  Further, in order to shift from the non-printing mode to the color mode, the drive motor 27 is driven and controlled to rotate the cam shaft 36, and the positions of the first eccentric cam 37 and the second eccentric cam 39 are shown in FIG. When rotated from the state shown in FIG. 6A to the state shown in FIG. 6A, both optical sensors 21a and 22a change from the OFF state to the ON state. Accordingly, by stopping the drive motor 27 at the timing when both the optical sensors 21a and 22a change from the OFF state to the ON state, all the photosensitive drums 3Y, 3M, 3C, and 3K are transferred to the intermediate transfer belt. It is possible to shift to the color mode state in contact with 61 without fail.

  In the above description, the mode transition from the color mode to the monochrome mode, from the monochrome mode to the non-printing mode, and from the non-printing mode to the color mode has been described. However, by rotating the cam shaft 36 in the reverse direction. Similarly, the mode transition from the color mode to the non-printing mode, from the non-printing mode to the monochrome mode, and from the monochrome mode to the color mode in the reverse direction can be surely performed by the ON / OFF state of both the optical sensors 21a and 22a. it can.

[Specific Example 2]
Although the specific example 1 is an example in which both the optical sensors 21a and 22a are used only as a toner density sensor and not used as a registration sensor, the specific example 2 is a case where both the optical sensors 21b and 22b are used as a toner density sensor. This is a specific example used for both the sensor and the resist sensor. Therefore, in particular, the arrangement position of the color optical sensor 22b is different from that of the first specific example.

  13 to 17 show the arrangement positions of the optical sensors 21b and 22b and the shapes of the shutters 51b and 52b according to the second specific example. FIG. 13 is a plan view of the intermediate transfer belt unit 6, and FIG. FIG. 15A is an enlarged perspective view of the shutter 51b portion, FIG. 15B is an enlarged perspective view of the shutter 52b portion, and FIGS. 15 to 17 are front views of the attachment / detachment mechanism 30 (30A).

  The optical sensor 21b of the second specific example functions as a toner density sensor that detects the toner density of each color of cyan (C), magenta (M), and yellow (Y), and as a registration sensor that detects the toner image formation position. The optical sensor 22b functions as a toner density sensor that detects the toner density of black (K) and also functions as a registration sensor that detects the toner image formation position. It is. Therefore, in the second specific example, both the color optical sensor 21b and the monochrome optical sensor 22b are arranged on the downstream side (right side in FIG. 15) of the photosensitive drum 3K. The color optical sensor 21 b is disposed in the vicinity of one side edge (lower side edge in FIG. 13) 611 of the intermediate transfer belt 61, and the monochrome optical sensor 22 a is the other side of the intermediate transfer belt 61. It is arranged near the side edge (upper side edge in FIG. 13) 612.

  On the other hand, the color shutter 51b that shields / opens the color optical sensor 21b is, as shown in FIGS. 13 and 14A, the first slide rod of one of the attachment / detachment mechanism portions 30A (lower side in FIG. 13). 35, a support piece 51b1 extending horizontally from the lower side near the right end 35a, a hanging piece 51b2 extending downward from the tip of the supporting piece 51b1, and a hanging piece 51b2 A horizontal piece 51b3 extending horizontally in the downstream direction (X1 direction) from the lower end and a light shielding piece 51b4 extending horizontally inward from the tip of the horizontal piece 51b3 are formed. In the color shutter 51b formed in this way, the base end side of the support piece 51b1 is fixed to the first slide rod 35 by screws or the like (not shown).

  Similarly, the monochrome shutter 52b that shields / opens the monochrome optical sensor 22b is, as shown in FIGS. 13 and 14B, the second slide of one separation / contact mechanism 30B (upper side in FIG. 13). A support piece 52b1 extending horizontally outward from the lower side near the right end 38b of the flange 38, a hanging piece 52b2 extending downward from the tip of the supporting piece 52b1, and the hanging piece 52b2 The light-shielding piece 52b3 extends horizontally inward from the lower end of the light. In the monochrome shutter 52b formed in this way, the base end side of the support piece 52b1 is fixed to the second slide rod 38 with a screw or the like (not shown). That is, the monochrome shutter 52b has the same shape as the monochrome shutter 52a of the first specific example.

  The light shielding pieces 51b4 and 52b3 of the shutters 51b and 52b formed in this way are arranged as shown in FIGS. 15 to 17 with respect to the optical sensors 21b and 22b.

  That is, FIG. 15 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the color mode state. In this color mode state, the color shutter 51b is in a state in which the color optical sensor 21b is opened, and the monochrome shutter 52b is in a state in which the monochrome optical sensor 22b is opened. That is, in the color mode state, both the optical sensors 21b and 22b are in the ON state. As a result, the color toner density and the toner image forming position can be detected by the color optical sensor 21b. That is, the color shutter 51b does not prevent the color optical sensor 21b from detecting the color toner density and the toner image formation position.

  FIG. 16 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the monochrome mode state. In the monochrome mode state, since only the first slide rod 35 moves in the X1 direction from the color mode state shown in FIG. 15, the color shutter 51b is in a state where the color optical sensor 21b is shielded from light. On the other hand, since the second slide rod 38 maintains its position, the monochrome shutter 52b opens the monochrome optical sensor 22b. That is, in the monochrome mode state, the color optical sensor 21b is in an OFF state and the monochrome optical sensor 22b is in an ON state. As a result, the black toner density and the toner image forming position can be detected by the monochrome optical sensor 22b. That is, the monochrome shutter 52b does not interfere with detection of the black toner density and the toner image forming position by the monochrome optical sensor 22b.

  FIG. 17 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the non-printing mode state. In this non-printing mode state, only the second slide rod 38 moves in the X2 direction from the monochrome mode state shown in FIG. 16, so the monochrome shutter 52b shields the monochrome optical sensor 22b. On the other hand, since the first slide rod 35 maintains its position, the color shutter 51b shields the color optical sensor 21b. That is, in the non-printing mode state, the color optical sensor 21b is OFF and the monochrome optical sensor 22b is OFF. That is, in the non-printing mode state, there is no problem because the toner density and the toner image forming position are not detected even if both the optical sensors 21b and 22b are in the OFF state.

  As described above, in the second specific example, the shutters 51b and 52b are arranged so as to be interlocked with the moving operation of the first slide rod 35 and the second slide rod 38 of the separation / contact mechanism 30 corresponding to each mode, The optical sensors 21b and 22b are shielded from light and opened so as not to prevent detection of the toner density and toner image formation position of the optical sensors 21b and 22b in the mode. As a result, as described above, in the color mode state, both the optical sensors 21b and 22b are in the ON state, and in the monochrome mode state, the color optical sensor 21b is in the OFF state, the monochrome optical sensor 22b is in the ON state, and the non-printing mode. In this state, since both the optical sensors 21b and 22b are in the OFF state, each of the photosensitive drums 3Y, 3M, 3C, and 3K and the intermediate transfer belt are detected by detecting the ON / OFF state of the optical sensors 21b and 22b. The separation / contact control with 61 can be performed. In addition, since the separation / contact control has been described in the specific example 1, description of the separation / contact control is omitted here.

[Specific Example 3]
In the specific examples 1 and 2, the optical sensors are arranged on the lower side of the intermediate transfer belt 61, that is, on the upstream side of the transfer roller 10 that performs the secondary transfer. The optical sensors 21 c and 22 c are arranged on the upper side of the intermediate transfer belt 61, that is, on the downstream side of the secondary transfer roller 10. Thereby, both optical sensors 21c and 22c can be used for both the toner density sensor and the registration sensor.

  18 to 23 show the arrangement positions of the optical sensors 21c and 22c and the shapes of the shutters 51c and 52c according to the third specific example, FIG. 18 is a plan view of the intermediate transfer belt unit 6, and FIG. 18 is a schematic sectional view taken along the line DD in FIG. 18, FIG. 20 is an enlarged perspective view of the shutter 51c portion, and FIGS.

  The optical sensor 21c of the third specific example functions as a toner density sensor that detects the toner density of each color of cyan (C), magenta (M), and yellow (Y), and as a registration sensor that detects the toner image formation position. The optical sensor 22c functions as a toner density sensor that detects the toner density of black (K) and also functions as a registration sensor that detects the toner image formation position. It is. The color optical sensor 21c is disposed near one side edge (lower side edge in FIG. 18) 611 of the intermediate transfer belt 61, and the monochrome optical sensor 22c is the other side edge of the intermediate transfer belt 61. Portion (in FIG. 18, the upper side edge portion) 612 is disposed in the vicinity.

  On the other hand, the color shutter 51c that shields and opens the color optical sensor 21c is, as shown in FIGS. 19 and 20A, the first slide rod of one of the attachment / detachment mechanism portions 30A (lower side in FIG. 18). 35, a support piece 51c1 extending horizontally outward from the upper side near the right end 35a, a vertical piece 51c2 extending upward from the tip of the support piece 51c1, and the vertical piece 51c2. The light shielding piece 51c3 extends horizontally inward from the upper end. However, in the color shutter 51c formed in this way, the base end side of the support piece 51c1 is fixed to the first slide rod 35 by screws or the like (not shown).

  Similarly, the monochrome shutter 52c that shields / opens the monochrome optical sensor 22c is, as shown in FIGS. 19 and 20B, the second slide of one of the contact mechanism portions 30B (upper side in FIG. 18). A support piece 52c1 extending horizontally from the upper side near the right end 38b of the flange 38, a vertical piece 52c2 extending upward from the tip of the support piece 52c1, and the vertical piece 52c2. And a light-shielding piece 52c3 that extends horizontally inward from the upper end of the light-emitting element. In the monochrome shutter 52c formed in this way, the base end side of the support piece 52c1 is fixed to the second slide rod 38 with a screw or the like (not shown). That is, the color shutter 51c and the monochrome shutter 52c have the same shape.

  The light shielding pieces 51c3 and 52c3 of the shutters 51c and 52c formed in this way are arranged as shown in FIGS. 21 to 23 with respect to the optical sensors 21c and 22c.

  That is, FIG. 21 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the color mode state. In this color mode state, the color shutter 51c is in a state where the color optical sensor 21c is opened, and the monochrome shutter 52c is in a state where the monochrome optical sensor 22c is opened. That is, in the color mode state, both the optical sensors 21c and 22c are both in the ON state. As a result, the color toner density and the toner image forming position can be detected by the color optical sensor 21c. That is, the color shutter 51c does not prevent the color optical sensor 21c from detecting the color toner density and the toner image forming position.

  FIG. 22 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the monochrome mode state. In the monochrome mode state, since only the first slide rod 35 moves in the X1 direction from the color mode state shown in FIG. 21, the color shutter 51c is in a state where the color optical sensor 21c is shielded from light. On the other hand, since the second slide rod 38 maintains its position, the monochrome shutter 52c opens the monochrome optical sensor 22c. That is, in the monochrome mode state, the color optical sensor 21c is OFF and the monochrome optical sensor 22c is ON. As a result, the black toner density and the toner image forming position can be detected by the monochrome optical sensor 22c. That is, the monochrome shutter 52c does not interfere with detection of the black toner density and the toner image forming position by the monochrome optical sensor 22c.

  FIG. 23 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the non-printing mode state. In the non-printing mode state, only the second slide rod 38 moves in the X2 direction from the monochrome mode state shown in FIG. 22, so that the monochrome shutter 52c shields the monochrome optical sensor 22c. On the other hand, since the first slide rod 35 maintains its position, the color shutter 51c shields the color optical sensor 21c. That is, in the non-printing mode state, the color optical sensor 21c is OFF and the monochrome optical sensor 22c is OFF. That is, in the non-printing mode state, there is no problem because the toner density and the toner image forming position are not detected even if both the optical sensors 21c and 22c are both OFF.

  As described above, in the third specific example, the shutters 51c and 52c are arranged so as to be interlocked with the movement operation of the first slide rod 35 and the second slide rod 38 of the separation / contact mechanism 30 corresponding to each mode. The optical sensors 21c and 22c are shielded from light and opened so as not to prevent detection of the toner density and toner image forming position of the optical sensors 21c and 22c in the mode. As a result, as described above, in the color mode state, both the optical sensors 21c and 22c are in the ON state, and in the monochrome mode state, the color optical sensor 21c is in the OFF state, the monochrome optical sensor 22c is in the ON state, and the non-printing mode. In this state, since both the optical sensors 21c and 22c are in the OFF state, each of the photosensitive drums 3Y, 3M, 3C, and 3K and the intermediate transfer belt are detected by detecting the ON / OFF state of the optical sensors 21c and 22c. The separation / contact control with 61 can be performed. In addition, since the separation / contact control has been described in the specific example 1, description of the separation / contact control is omitted here.

[Specific Example 4]
In the third specific example, in order to make the shapes of the shutters 51c and 52c provided on the first slide rod 35 and the second slide rod 38 of the separation / contact mechanism 30 the simplest shape, the arrangement of the optical sensors 21c and 22c is arranged. The positions are shifted from each other in the moving direction of the intermediate transfer belt 61 so as to face each other. However, as an actual arrangement, it is preferable to arrange them in the direction orthogonal to the moving direction of the intermediate transfer belt 61. The fourth specific example is an example in which the optical sensors 21 c and 22 c are arranged to face each other along the cam shaft 36.

  24 to 28 show the arrangement positions of the optical sensors 21d and 22d and the shapes of the shutters 51d and 52d according to the fourth specific example. FIG. 24 is a plan view of the intermediate transfer belt unit 6, and FIG. FIG. 26A is an enlarged perspective view of the shutter 51d portion, FIG. 26B is an enlarged perspective view of the shutter 52d portion, and FIGS.

  The optical sensor 21d of the fourth specific example functions as a toner density sensor that detects the toner density of each color of cyan (C), magenta (M), and yellow (Y), and as a registration sensor that detects the toner image formation position. The optical sensor 22d functions as a toner density sensor that detects the toner density of black (K) and also functions as a registration sensor that detects the toner image formation position. It is. The color optical sensor 21d is disposed near one side edge (lower side edge in FIG. 24) 611 of the intermediate transfer belt 61, and the monochrome optical sensor 22d is the other side edge of the intermediate transfer belt 61. Portion (upper side edge portion in FIG. 24) 612 is disposed in the vicinity.

  On the other hand, the color shutter 51d that shields and opens the color optical sensor 21d is, as shown in FIG. 25A, the right side of the first slide rod 35 of one separation / contact mechanism 30A (lower side in FIG. 24). A support piece 51d1 extending horizontally outward from the upper side near the end 35a, a vertical piece 51d2 extending upward from the tip of the support piece 51d1, and an upper end of the vertical piece 51d2 A horizontal piece 51d3 extending horizontally inward and a light-shielding piece 51d4 extending from one edge side of the horizontal piece 51d3 to the upstream side of the intermediate transfer belt 61 are formed. However, in the color shutter 51d formed in this way, the base end side of the support piece 51c1 is fixed to the first slide rod 35 by screws or the like (not shown).

  Similarly, a monochrome shutter 52d that shields and opens the monochrome optical sensor 22d is provided on the second slide rod 38 of one separation / contact mechanism 30B (upper side in FIG. 24) as shown in FIG. A support piece 52d1 extending horizontally outward from the upper side near the right end 38b, a vertical piece 52d2 extending upward from the tip of the support piece 52d1, and an upper end of the vertical piece 52d2 And a light shielding piece 52d4 extending from one edge side of the horizontal piece 52d3 to the downstream side of the intermediate transfer belt 61. In the monochrome shutter 52d formed in this way, the base end side of the support piece 52d1 is fixed to the second slide rod 38 with a screw or the like (not shown). That is, the color shutter 51d and the monochrome shutter 52d have substantially the same shape.

  The light shielding pieces 51d4 and 52d4 of the shutters 51d and 52d formed as described above are arranged as shown in FIGS. 26 to 28 with respect to the optical sensors 21d and 22d.

  That is, FIG. 26 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the color mode state. In this color mode state, the color shutter 51d is in a state where the color optical sensor 21d is opened, and the monochrome shutter 52d is in a state where the monochrome optical sensor 22d is opened. That is, in the color mode state, both the optical sensors 21d and 22d are in the ON state. Thus, the color toner density and the toner image forming position can be detected by the color optical sensor 21d. That is, the color shutter 51d does not prevent the color optical sensor 21d from detecting the color toner density and the toner image forming position.

  FIG. 27 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the monochrome mode state. In the monochrome mode state, only the first slide rod 35 moves in the X1 direction from the color mode state shown in FIG. 26, so that the color shutter 51d shields the color optical sensor 21d. On the other hand, since the second slide rod 38 maintains its position, the monochrome shutter 52d opens the monochrome optical sensor 22d. That is, in the monochrome mode state, the color optical sensor 21d is in the OFF state and the monochrome optical sensor 22d is in the ON state. As a result, the black toner density and the toner image forming position can be detected by the monochrome optical sensor 22d. That is, the monochrome shutter 52d does not interfere with detection of the black toner density and the toner image forming position by the monochrome optical sensor 22d.

  FIG. 28 shows the arrangement positions of the first slide rod 35 and the second slide rod 38 in the non-printing mode state. In the non-printing mode state, only the second slide rod 38 moves in the X2 direction from the monochrome mode state shown in FIG. 27, so that the monochrome shutter 52d shields the monochrome optical sensor 22d. On the other hand, since the first slide rod 35 maintains its position, the color shutter 51d shields the color optical sensor 21d. That is, in the non-printing mode state, the color optical sensor 21d is OFF and the monochrome optical sensor 22d is OFF. That is, in the non-printing mode state, there is no problem because the toner density and the toner image forming position are not detected even when both the optical sensors 21d and 22d are in the OFF state.

  As described above, in the fourth specific example, the shutters 51d and 52d are arranged so as to be interlocked with the moving operation of the first slide rod 35 and the second slide rod 38 of the separation / contact mechanism 30 corresponding to each mode. The optical sensors 21d and 22d are shielded from light and opened so as not to prevent detection of the toner density and toner image forming position of the optical sensors 21d and 22d in the mode. As a result, as described above, in the color mode state, both the optical sensors 21d and 22d are in the ON state, and in the monochrome mode state, the color optical sensor 21d is in the OFF state, the monochrome optical sensor 22d is in the ON state, and the non-printing mode. In this state, since both the optical sensors 21d and 22d are in the OFF state, each of the photosensitive drums 3Y, 3M, 3C, and 3K and the intermediate transfer belt are detected by detecting the ON / OFF state of the optical sensors 21d and 22d. The separation / contact control with 61 can be performed. In addition, since the separation / contact control has been described in the specific example 1, description of the separation / contact control is omitted here.

  In the case of the specific examples 3 and 4, the optical sensors 21c, 22c and 21d, 22d are arranged on the downstream side of the transfer roller 10, so that the toner density and the toner image forming position are detected. The transfer roller 10 is separated from the intermediate transfer belt 61 so that the toner images transferred to the intermediate transfer belt 61 by the photosensitive drums 3Y, 3M, 3C, and 3K are not secondarily transferred by the transfer roller 10. There is a need. FIG. 29 to FIG. 31 show an example of the separation / contact structure of the transfer roller 10.

  In this example, the secondary transfer unit 131 including the transfer roller 10 is attached to the side unit 121 disposed on the intermediate transfer belt 61 on the intermediate transfer belt driving roller 62 side.

  The side unit 121 can be pulled out (in the direction of the arrow X1 in the drawing) and mounted (in the direction of the arrow X2 in the drawing) by the guard rails 122 and 123 provided on the device frame (not shown). It is provided to slide.

  The secondary transfer unit 131 includes a rotating plate 133 whose lower end is rotatably attached to the side unit 121 by a support shaft 132. The transfer roller 10 is rotated on the lower side of the rotating plate 133. A roller housing 134 is held so as to be held. That is, the transfer roller 10 can be brought into contact with and separated from the intermediate transfer belt 61 wound around the intermediate transfer belt driving roller 62 by the rotation operation of the rotation plate 133 around the support shaft 132. ing.

  On the other hand, the upper side of the rotating plate 133 is a cam contact surface 135 bulged toward the intermediate transfer belt unit 6, and the cam shaft 136 is located at the end of the side unit 121 on the intermediate transfer belt unit 6 side. Thus, it comes into contact with the cam surface of the eccentric cam 137 held rotatably. Further, an elastic member 138 such as a coil spring for urging the cam contact surface 135 to contact the cam surface of the eccentric cam 137 between the surface opposite to the cam contact surface 135 and the side unit 121. Is intervening. By this elastic member 138, the cam contact surface 135 of the rotating plate 133 is always in contact (pressure contact) with the cam surface of the eccentric cam 137.

  When the cam contact surface 135 is in contact with the cam surface closest to the cam center of the eccentric cam 137 (the state shown in FIG. 29), the transfer roller 10 is at a predetermined nip pressure and the intermediate transfer belt. It arrange | positions so that 61 may be contact | abutted. In addition, the transfer roller 10 is separated from the intermediate transfer belt 61 in a state where the cam contact surface 135 is in contact with the cam surface that is farthest from the cam center of the eccentric cam 137 (the state shown in FIG. 30). It has become.

  On the other hand, when the side unit 121 is pulled out from the apparatus main body in the X1 direction in order to remove the intermediate transfer belt unit 6, the eccentric cam 137 moves in the X1 direction together with the side unit 121 as shown in FIG.

  In the above configuration, the transfer roller 10 and the eccentric cam 137 are in the positional relationship shown in FIG. 29 when the image forming apparatus 100 is in a normal operation (image forming operation). That is, the cam contact surface 135 of the rotating plate 133 is in contact with the cam surface closest to the cam center of the eccentric cam 137, and the transfer roller 10 is disposed in contact with the intermediate transfer belt 61 with a predetermined nip pressure. Has been.

  On the other hand, when the eccentric cam 137 is rotated 180 degrees in one direction (either right direction or left direction) by the driving means (not shown) from the state shown in FIG. 29, as shown in FIG. 30, the cam of the rotating plate 133 The contact surface 135 is in contact with the cam surface that is farthest from the cam center of the eccentric cam 137, and as a result of the rotation plate 133 swinging in the X1 direction by the amount of eccentricity of the eccentric cam 137, the transfer roller 10 is moved. Is separated from the intermediate transfer belt 61. Therefore, in the specific examples 3 and 4, when the toner density detection and the toner image formation position are detected by the optical sensors 21c, 22c and 21d, 22d, as shown in FIG. The transfer roller 10 can be separated from the intermediate transfer belt 61 by setting the contact surface 135 in contact with the cam surface that is farthest from the cam center of the eccentric cam 137.

  When the intermediate transfer belt unit 6 is replaced, the side unit 121 is pulled out from the apparatus main body in the X1 direction as shown in FIG. As a result, the transfer roller 10 is also greatly separated from the intermediate transfer belt 61.

  Next, the optical sensors 21 and 22 will be described. These optical sensors 21 and 22 have the same structure. FIG. 32 shows an arrangement state of these optical sensors 21 and 22 with respect to the intermediate transfer belt 61. However, FIG. 32 is a simplified diagram illustrating only one optical sensor.

  The optical sensors 21 and 22 include an LED 231 that is a light emitting element, a phototransistor 232 that is a monochrome light receiving element that receives specularly reflected light, and a phototransistor 233 that is a color light receiving element that receives irregularly reflected light. The infrared light from the LED 231 is reflected by the toner image 68 on the intermediate transfer belt 61 and detected by the phototransistor 232 or 233, thereby detecting the monochrome toner density and the color toner density and reflecting them in the process control. (See FIG. 32 (a)). When the toner image 68 is not formed, the reflected light from the intermediate transfer belt 61 can be detected by the phototransistor 222 (see FIG. 32B).

  On the other hand, as shown in FIG. 11, in the monochrome mode state in which the intermediate transfer belt 61 is separated from the photosensitive drums 3Y, 3M, and 3C, a shutter 51 is interposed between the intermediate transfer belt 61 and the optical sensor 21, The optical sensor 21 is shut off (see FIG. 32C). On the other hand, although not shown, the other optical sensor 22 is open. As a result, it can be detected that the intermediate transfer belt 61 is in the monochrome mode separation state.

  FIG. 33 shows a peripheral circuit configuration of the present apparatus including the optical sensors 21 and 22. However, FIG. 33 shows a circuit configuration of only a main part according to the present invention.

  A control unit 75 including a CPU, ROM, RAM, and the like (not shown) is connected to the LEDs 231 of the optical sensors 21 and 22 via the D / A converter 76, and is connected to the optical sensors via the A / D converter 77. 21 and 22 are connected to the phototransistors 232 and 233, respectively. That is, each LED 231 has a cathode connected to the ground potential and an anode connected to the D / A converter 76 via the resistor R1. Each of the phototransistors 232 and 233 has an emitter connected to the ground potential, a collector connected to the power supply voltage Vcc via the resistor R2, and an A / D converter 77. The A / D converter 77 converts the analog output of each phototransistor 232, 233 into a digital value. The control unit 75 controls the D / A converter 76 based on the digital value from the A / D converter 77 that is the output of each phototransistor 232 and 233 so as to adjust the irradiation light amount of each LED 21 and 22. It has become. The control unit 75 is connected to a drive motor 27 linked to the cam shaft 36 of the separation / connection mechanism unit 30.

  Further, a mode control signal is input to the controller 75 from a main controller (not shown) that controls the operation of the color image forming apparatus main body. Based on this mode control signal, the control unit 75 controls the separation / contact mechanism unit 30 to change the state of the intermediate transfer belt 61 to, for example, a color mode, a monochrome mode, or a non-printing mode. Or

  The control unit 75 determines these modes based on the outputs from the optical sensors 21 and 22.

  That is, if both the optical sensors 21 and 22 are in the ON state, it is determined that the color mode is in the state shown in FIG. 10 of the first specific example, for example, the color optical sensor 21 is in the OFF state, and the monochrome optical sensor 22 is If it is in the ON state, for example, it is determined that the monochrome mode shown in FIG. 11 of Specific Example 1 is set. If both the optical sensors 21 and 22 are in the OFF state, for example, in the non-printing mode shown in FIG. Judge that there is. The control unit 75 drives the drive motor 27 to control the rotation of the camshaft 36 and always determines the ON / OFF state of both the optical sensors 21 and 22 and determines which of the intermediate transfer belt 61 is based on the determination result. By detecting whether it is in the state, the intermediate transfer belt unit 6 can be controlled to each operation mode.

1 is a front view showing an overall configuration of a color image forming apparatus of the present invention. 1 is a front view showing a peripheral structure of an intermediate transfer belt unit according to the present invention, in particular, a basic structure of a separation / contact mechanism portion of an intermediate transfer belt. 1 is a front view showing a peripheral structure of an intermediate transfer belt unit according to the present invention, in particular, a basic structure of a separation / contact mechanism portion of an intermediate transfer belt. 1 is a front view showing a peripheral structure of an intermediate transfer belt unit according to the present invention, in particular, a basic structure of an intermediate transfer belt separation / contact mechanism portion. FIG. 3 is a plan view showing a peripheral structure of the intermediate transfer belt unit according to the present invention, in particular, a basic structure of an intermediate transfer belt separation / contact mechanism portion. It is explanatory drawing which shows the shape and arrangement | positioning positional relationship of the 1st eccentric cam and 2nd eccentric cam which were integrally formed in the cam shaft. FIG. 6 is a plan view of an intermediate transfer belt unit showing an arrangement position of an optical sensor and a shape of a shutter according to Example 1 of the present invention. It is a schematic sectional drawing in alignment with the AA in FIG. (A), (b) is an expansion perspective view of a shutter part. FIG. 3 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 1 of the invention. FIG. 3 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 1 of the invention. FIG. 3 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 1 of the invention. FIG. 10 is a plan view of an intermediate transfer belt unit showing an arrangement position of an optical sensor and a shape of a shutter according to Example 2 of the present invention. (A), (b) is an expansion perspective view of a shutter part. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 2 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 2 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 2 of the invention. FIG. 10 is a plan view of an intermediate transfer belt unit showing an arrangement position of an optical sensor and a shape of a shutter according to Example 3 of the present invention. It is a schematic sectional drawing which follows the DD line | wire in FIG. (A), (b) is an expansion perspective view of a shutter part. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 3 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 3 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism according to Example 3 of the invention. FIG. 10 is a plan view of an intermediate transfer belt unit showing an arrangement position of an optical sensor and a shape of a shutter according to Example 4 of the present invention. (A), (b) is an expansion perspective view of a shutter part. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 4 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 4 of the invention. FIG. 10 is a front view of an intermediate transfer belt including a separation / contact mechanism portion according to Example 4 of the invention. It is a front view which shows the separation-contact mechanism structure of a transfer roller. It is a front view which shows the separation-contact mechanism structure of a transfer roller. It is a front view which shows the separation-contact mechanism structure of a transfer roller. It is explanatory drawing which shows the state of an optical sensor vicinity. It is a peripheral circuit block diagram of this apparatus containing an optical sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure unit 2 Developing device 3 Photoconductor drum 4 Cleaner unit 5 Charger 6 Intermediate transfer belt unit 7 Fixing unit 10 Transfer roller 11a, 11b Pickup roller 12a-12d Conveyance roller 13 Registration roller 21, 21a-21d Optical sensor (for color) Optical sensor)
22, 22a-22d Optical sensor (monochrome optical sensor)
25 1st gear 26 2nd gear 27 Drive motor 30 (30A, 30B) Separation / contact mechanism 31, 33 Transfer roller arm 31a, 33a Armband (horizontal armband)
31b, 33b Bent part 31c, 33c Armband (longitudinal armband)
32 First spring 35 First slide rod 35a Right end 36 Cam shaft 37 First eccentric cam 37a Swelling portion (large diameter portion)
37b Small diameter portion 38 Second slide rod 38a Left end portion 38b Right end portion 39 Second eccentric cam 39a Swelling portion (large diameter portion)
39b Small-diameter portion 43 Backup roller arm 43a Armband (horizontal armband)
43b bent part 43c armband (longitudinal armband)
51, 51a to 51d Shutter (color shutter)
52, 52a to 52d Shutter (monochrome shutter)
61 Intermediate transfer belt 62 Intermediate transfer belt drive roller 63 Intermediate transfer belt driven roller 64 Intermediate transfer roller 65 Intermediate transfer belt cleaning unit 66 Backup roller 68 Toner image 71 Heat roller 72 Pressure roller 75 Controller 76 D / A converter 77 A / D converter 81 Paper feed cassette 82 Manual paper feed cassette 91 Paper discharge tray 92 Document placement table 100 Color image forming apparatus 110 Apparatus main body 121 Side unit 122, 123 Guard rail 131 Secondary transfer unit 132 Support shaft 133 Rotating plate 135 Cam Contact surface 136 Cam shaft 137 Eccentric cam 138 Elastic member (unit biasing means)
120 Automatic document processing device

Claims (8)

A plurality of photosensitive drums carrying toner images; an intermediate transfer belt that superimposes a plurality of color toner images on each photosensitive drum; and a contact that separates and contacts the intermediate transfer belt and each photosensitive drum. A color image forming apparatus comprising: a contact mechanism; and an optical sensor that detects reflected light from the toner image on the intermediate transfer belt.
A shutter that shields and opens the optical sensor in conjunction with the operation of the separation mechanism;
A color image comprising: a contact / separation control unit that controls contact / separation between the intermediate transfer belt and each of the photosensitive drums based on an output from the optical sensor by a light shielding / opening operation of the shutter. Forming equipment. The color image forming apparatus according to claim 1.
The color image forming apparatus, wherein the separation / contact control unit controls separation / contact between the intermediate transfer belt and each of the photosensitive drums in three modes of a color mode, a monochrome mode, and a non-printing mode. The color image forming apparatus according to claim 1 or 2,
When the shutter moves to a position where the optical sensor shields the optical sensor, the separation / contact mechanism portion moves the intermediate transfer belt away from the photosensitive drum in association with the movement, and the shutter opens the optical sensor. The color image forming apparatus, wherein the intermediate transfer belt is brought into contact with the photosensitive drum in association with the movement . The color image forming apparatus according to claim 2.
The separation / contact control unit brings all the photosensitive drums into contact with the intermediate transfer belt in the color mode, contacts only the black photosensitive drum with the intermediate transfer belt in the monochrome mode, and all in the non-printing mode. A color image forming apparatus, wherein the photosensitive drum is separated from the intermediate transfer belt. The color image forming apparatus according to any one of claims 1 to 4, wherein:
The color image forming apparatus, wherein the shutter is provided on a lever of the separation / contact mechanism that moves in parallel with the moving direction of the intermediate transfer belt. The color image forming apparatus according to any one of claims 1 to 5, wherein:
The optical sensor includes a monochrome optical sensor that detects black toner density and a color optical sensor that detects toner density of colors other than black toner, and the shutter is provided in each optical sensor. A color image forming apparatus. The color image forming apparatus according to any one of claims 1 to 5, wherein:
The optical sensor includes a monochrome optical sensor for detecting a black toner density and a toner image forming position, and a color optical sensor for detecting a toner density of a color other than black toner and a toner image forming position , and the shutter. Is provided in each optical sensor. The color image forming apparatus according to any one of claims 1 to 7,
A color image forming apparatus, wherein the optical sensor is a reflective sensor.

Images